The present invention relates to code scanning devices and, in particular, to apparatus and methods for restoring a code from differing code fragments.
Well known equipment exists for reading a bar code that is printed on a package. Bar codes on merchandise may be scanned at the point of sale to identify the goods and correlate them to a price. Such equipment is commonly used at supermarket checkout counters.
A basic principle conventionally applied in bar code scanning is that of detecting reflected light contrasts. A source of illumination such as a low powered helium neon laser, can produce a beam which is moved across the bar code. Dark areas (bars) absorb laser light, whereas light areas (spaces) reflect light that is subsequently detected by the scanner.
Optics are used to "move" a laser beam. Without these optics, the laser beam appears as a dot. When the optics are used, the beam appears as a line of laser light. This is defined as moving-beam scanning. As the moving beam "travels" across the conveyor (or area to be scanned for a code, commonly called the scanning zone) any light or dark transitions are detected and converted to a digital signal known as code. A valid bar code consists of a defined number of light and dark transitions with correct ratios between the wide and narrow intervals.
Existing codes consist of a series of parallel bars separated by spaces. The bars and spaces are printed at either a full width or half width. The bars and spaces may signify a bit pattern wherein wide spaces or bars are denominated a "one" while narrow spaces and bars are denominated a "zero" (or vice versa).
A basic objective in known bar code scanning is laying down a trace that is dense and varied enough to ensure that at least one scan will recover a complete bar code. The denser the scanning, the more rapidly scanning must occur and, therefore, a higher demand is placed upon the circuitry processing the scanned data.
Known equipment (for example, U.S. Pat. No. 3,728,677) employs a mirrored wheel having a polygonal periphery. Rotation of the mirrored wheel scans a laser beam across two azimuthally spaced mirrors which deflect the beam downwardly to trace an "X" shaped pattern.
Other known equipment has used prisms, mirrors, vidicons, or other apparatus to turn the scan direction of an optical code scanning system. (See, for example, U.S. Pat. Nos. 3,663,800; 3,774,014; 3,800,282; 3,902,047; and 4,064,390).
It is also known (U.S. Pat. No. 3,906,203) to scan a bar code and measure its interval widths by recording the time required to traverse each interval. The successive interval widths are multiplied by three, five, and eight. By storing and comparing the multiplied widths of successive scans, the equipment can determine whether the latest interval is about the same size as, or much smaller or larger than, the prior interval. This equipment, however, performs a relatively coarse comparison and will accept as valid, scan times that are excessively short or long.
Accordingly there is a need for a code scanner that does not require support from extraordinarily high speed circuitry, but yet has a high probability of obtaining a complete code when an object passes by the scanner.